For acquiring the arterial response to the pulsating blood flow by noninvasive blood pressure measurement with a cuff, a pressurizing unit and bleeding valves, there have been the following available methods: displaying only the intensity level of the Korotkoff's sounds graphically by using a microphone, and displaying the cuff's oscillating pressure wave whose constant bleeding rate is filtered out.
However, there do not exist blood pressure measurement devices which display, in real time, information on the response to the pulsating blood flow and the bleeding of the cuff's pressure while simultaneously displaying the simulated mercury and aneroid manometers.
The invention resolves the following problems of prior measurement devices. Using current methods with a microphone, the acquired dynamic response of an artery to pulsating blood flow does not include information on arterial wall motion. That undetected motion includes movement that creates and annihilates the Korotkoff's sounds, movement immediately before and after the sounds, and movement not creating any Korotkoff's sounds.
The response to the pulsating blood flow which is obtained with the AC component of the cuff's pressure after filtering its DC component can show only the trend of the magnitude variation of the cuff's pressure oscillation. But the response cannot show the dynamic expansion rate of the arterial wall. Furthermore, the arterial response to pulsating blood flow from which the systolic and the diastolic pressure are determined varies with the environment in which a subject is placed and the individual characteristics of the subject. Obtaining accurate systolic and diastolic readings for various subjects is difficult from judging only the trend of the magnitude of the cuff's pressure oscillation.
A method of acquiring the arterial response to pulsating blood flow is described in Japanese patent applications No. 61-118305 and No. 61-276785. The applications describe a filtering method. The method takes the first derivative of the cuff's pressure and then its integration with respect to time to obtain the increased amount of the cuff's pressure caused by the arterial expansion against the cuff's pressure. Thus, it merely increases the accuracy of the filtering of the oscillating pressure. Since this integration is carried on with the first derivatives above a constant threshold value, it is easily affected by a small change in the bleeding rate.
Difficulty often arises in displaying the graphics of the dynamic parameters characterizing the expansion of the arterial wall, namely the displacement velocity of the wall and the parameters related to its acceleration change.
Therefore, with the bleeding rate nearly constant or even changing, this invention acquires the time trend of the artery wall's expansion caused by the pressure fluctuation in pulsating blood flow against the cuff pressure, acquires the wall motion that gives the accurate systolic and diastolic pressure, and monitors the arterial response to the pulsating blood flow.
Another difficulty in noninvasive blood pressure measurements is obtaining the regulated constant bleeding rate and monitoring the change in the bleeding rate over time. In subjects, the detection of Korotkoff's sounds in phases 1, 4 or 5 often becomes difficult, depending on the magnitude of the bleeding rate. Furthermore, the physical and psychological surroundings of a subject alter one's normal systolic and diastolic pressure readings significantly. In these cases, medical personnel using current auscultatory blood pressure measuring methods have difficulty in determining the cause for the changes.
In U.S. Pat. No. 5,222,020, there is described a blood pressure measuring apparatus which is coupled with an occlusive cuff in order to acquire dynamics on a pulsatile wall motion of human artery responding to the occlusive cuff as its pressure is lowered. The instantaneous cuff pressure (Pc) is first obtained with a pressure transducer; then its value is displayed on a CRT in real time as height variations of mercury nanometer along with the dynamic parameters describing the pulsatile wall motion. The dynamic parameters are basically its displacement velocity and acceleration of the motion generated by blood flow pulsating against the lowering Pc, which reflects the mechanical cardiac cycle of heart as reported by F. Takeda, et al., in Med. Bio. Eng. Comput., Vol. 29, Supplement Part 1, 1991 which is hereby incorporated by reference.
In the commonly practiced noninvasive measurements with a pressure cuff and a bleeding valve controlling a quiet and constant deflation of cuff pressure Pc, without auscultation of Korotkoff sounds (KS) during their various phases, one may be obliged to use the oscillometric method to estimate systolic pressure (SYS), mean pressure (MEAN) and diastolic pressure (DIA) of human brachial artery. Its principle is that the oscillations of Pc which are transmitted by the arterial wall motion synchronizing with pulsatile artery blood pressure have their unique oscillation amplitudes (displacement amplitudes); for example, a sudden increase in their amplitudes when cuff pressure Pc unsynchronously gets to one of the arterial pressure pulse wave crests, their maximum amplitude, and a sudden decrease in their amplitudes when Pc unsynchronously approaches one of the pressure pulse wave troughs are used to detect SYS, MEAN and DIA, respectively, as reported by K. M. Borow et al., in Am. Heart J., Vol. 103, 1982. Since these sudden increases and decreases are very fuzzy, various techniques to determine SYS and DIA have been developed by T. W. Russell, described in U.S. Pat. No. 4,718,428, January 1988, D. E. Bahr et al., described in U.S. Pat. No. 4,796,184, January 1989, and Y. Miyawaki, et al., described in U.S. Pat. No. 4,793,360, December 1988.
As for detecting SYS and DIA in the present invention, no such analyses of fuzzy oscillation amplitudes are used. Instead, the dynamic parameters describing arterial wall motion are used. The use of some dynamic parameters to detect SYS and DIA will be made not only for quietly lowering Pc, but also for inflating Pc with a mechanical pump which produces noisy pressure fluctuations comparable with those due to arterial wall motion. This last feature to detect SYS while inflating Pc in automatic blood pressure measuring apparatus is very useful. This is because a pain which subjects often feel with the cuff pressure being inflated far above his or her own SYS can be greatly reduced.
Thus, one object of the invention is to resolve the difficulties stated above by displaying in real time the bleeding of the cuff's pressure during the blood pressure measurements as well as displaying the simulated mercury manometer.
A further object of the invention is the measuring and monitoring of the arterial response in nearly real time for those subjects remote from clinics or hospitals.